1. Field of the Invention
The present invention relates to a reactive power compensator including a static var compensator that compensates for reactive power to suppress voltage fluctuation in a power system.
2. Description of the Related Art
In the past, a reactive power compensator is used as one of control systems for stabilizing the voltage of a power system. The reactive power compensator includes a static var compensator (SVC) that compensates for reactive power with respect to voltage fluctuation in the power system and a reactive power controller that controls reactive power output by the SVC.
In some case, the reactive power compensator includes a phase modifying equipment connected to the power system in parallel to the SVC. The phase modifying equipment includes one of a static capacitor (SC) and a shunt reactor (ShR) or both. The phase modifying equipment can compensate for reactive power by closing or opening the power system via a breaker.
The SVC controls a switch formed by a semiconductor element and generates leading or lagging reactive power. The SVC can instantaneously and continuously control the reactive power. On the other hand, because the phase modifying equipment is connected to the power system via the breaker, the phase modifying equipment discontinuously limits the reactive power according to operation for turning on and off the breaker. However, an adjustment range of the reactive power can be set larger than that in operation by only the SVC.
In the past, the reactive power compensator does not perform control assuming sudden voltage fluctuation. The reactive power compensator is often operated in a state in which the SVC generates reactive power equivalent to most of the capacity of the SVC in the steady state. Therefore, if sudden voltage fluctuation occurs during disturbance of the power system in the state in which the SVC generates reactive power equivalent to most of the capacity of the SVC, in some case, the SVC cannot sufficiently generate reactive power necessary for suppressing the voltage fluctuation and cannot suppress the voltage fluctuation. Therefore, for example, a reactive power compensator disclosed in Japanese Patent Application Laid-open No. 2008-40733 allots reactive power to the phase modifying equipment to control reactive power output by the SVC during steady operation to near zero and performs control corresponding to occurrence of disturbance of the power system.
In Japanese Patent Application Laid-open No. H04-333112, when two SVCs are arranged close to each other, the operations of the SVCs are coordinated by calculating a current deviation of one SVC and inputting a result of the calculation to a control device of the other SVC to correct an output of the other SVC.
However, in the reactive power compensator in the past, for example, when the two SVCs are arranged close to each other, the respective SVCs quickly suppress voltage fluctuation of the power system. Therefore, in some case the SVCs cannot output proper reactive power. When the phase modifying equipment is further provided, for example, unnecessary closing or opening of the static capacitor or the shunt reactor occurs.
As an example of measures against the problem, in Japanese Patent Application Laid-open No. H04-333112, the operations of the two SVCs are balanced by performing control for calculating a current deviation of one SVC and inputting a result of the calculation to the control device of the other SVC to correct an output of the other SVC. However, in such a control method, it is necessary to provide, separately from the SVCs and the control device of the SVC, a control unit having a function of calculating a current deviation. Therefore, the configuration of the reactive power compensator is complicated.